Chapter 2, Sexual Reproduction in Flowering Plants
CBSE Board, Class XII Biology - NCERT Answers of Chapter Exercise Questions
To see answers of exercise question no 1 - 10 of Chapter 2, Sexual Reproduction in Flowering Plants, click - Chapter 2, Sexual Reproduction in Flowering Plants - CBSE Class 12 Biology - NCERT Solutions
Question 11: What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer: Triple Fusion: It is the process of fusion of three nuclei, two polar nuclei (fuse to form a diploid secondary nucleus) and a male gamete. It was reported by Nawaschin in Lilium and Fritallaria.
Triple fusion occurs in the embryo sac of the ovule of angiosperms. The nuclei involved are two polar nuclei and a male gamete.
Question 12: Why do you think the zygote is dormant for sometime in a fertilised ovule?
Answer: Since, the zygote develops only after a certain amount of endosperm is formed to assure nutrition to the developing embryo, zygote is said to be dormant for this of period.
Question 13: Differentiate between:
(a) hypocotyl and epicotyl;
(b) coleoptile and coleorrhiza;
(c) integument and testa;
(d) perisperm and pericarp
1. The part of the embryonic axis present below the cotyledon is called "hypocotyl".
2. Hypocotyl terminates with root cap called radical.
3. It elongates faster during epigeal germination.
1. The part of the embryonic axis present above the cotyledon is called "epicotyl".
2. Epicotyl terminates with stem tip called plumule.
3. It elongates faster during hypogeal germination.
1. Coleoptile is the foliaceous sheath that covers the plumule in the embryo of cereals.
2. It belongs to the shoot system.
Fig: V. S. of Maize Grain
1. Coleorrhiza is the protective covering of the radical in the embryo of the cereals.
2. It belongs to the root system.
1. It is the protective covering of ovule.
2. It encircles the ovule completely except at micropylar end. They are protective in nature.
3. It develops into the seed coat.
1. Testa is the outer covering of a seed.
2. Testa is hard and provides protection to the young embryo. Micropyle is also present here.
3. It develops from the outer integument.
1. Perisperm is the remnant of the nucellus (of ovule) in the seed.
2. It is a single layer to store food.
3. It is a part of the seed.
1. Pericarp is the wall of fruit formed by the ovary wall.
2. It may be divided into three layers viz exocarp, mesocarp and endocarp.
3. It is a part of the fruit.
Question 14: Why is the apple called a false fruit ? Which parts of the flower forms the fruit ?
Answer: A fruit is a matured ovary with or without seeds. If any part of a flower other than the ovary becomes a part of the fruit, the fruit is a false fruit.
In apple, the thalamus grows over the true fruit and becomes fleshy and edible. The true fruit lies within it. It has an inferior ovary, two or more seeded and fleshy syncarpous fruit surrounded by thalamus. It is known as pome.
Question 15: What is meant by emasculation ? When and why does a plant breeder employ this technique ?
Removal of anther in bud condition from a bisexual flower of female parent is called "emasculation". Emasculation is not required in the female parent if it produces unisexual flower. It is done manually by using forceps.
A plant breeder employs this technique for the following reasons:
1. To produce commercially superior varieties of plants.
2. When the flower to be used as female parent is bisexual.
3. To prevent self- pollination or contamination of the stigma with the self-pollen.
4. To produce desired cross-pollination between different species.
5. To combine desirable characters.
6. It is followed by bagging.
Question 16: If one can induce parthenocarpy through the application of growth substances, which fruits you would select to induce parthenocarpy and why ?
Answer: The term "parthenocarpy" was coined by Knoll. The development of fruits without fertilisation is called "parthenocarpy". Parthenocarpic fruits are seedless, e.g., banana. Parthenocarpy can be induced with the help of growth regulators like- Gibberellins (GA3), Auxins (IBA). It can be natural or induced.
The fruits which I would select to induce parthenocarpy are- grapes, oranges, lemons, etc because it is easy for the preparation of juicy fruit and also they are very successful commercially.
Question 17: Explain the role of tapetum in the formation of pollen-grain wall.
Answer: Tapetum is the innermost wall layer of a microsporangium, where cells are large, densely cytoplasmic and may be binucleate. The various roles played by tapetum are as follows:
1. It acts as a nutritive layer i.e., provides nourishment to pollen.
2. They store food material.
3. Secretion of hormones and various enzymes.
4. Transportation of nutrients in anther locule during meiosis in spore mother cells.
5. Production of Ubisch bodies coated with sporopollenin to cause exine thickening.
6. Secretion of pollenkit (oily substance) outside mature pollen.
7. Secretion of proteins for pollen to be compatible during recognisition.
Question 18: What is apomixes? What is its importance ?
It is a special type of asexual reproduction that mimics sexual reproduction. Development of embryo / seeds without fertilisation is called "apomixes". The term "apomixes" was coined by Wrinkler.
Importance of Apomixes: Apomixes is very important in agriculture as given hereunder -
1. Problems of Hybrid Seed Industry
(a) Hybrid seeds had to be produced in every year. The progeny of hybrid seeds sdo not maintain hybrid (desirable) characters. Hence, characters become unstable. It is due to seggregation of characters.
(b) It occurs during meiosis & sexual reproduction.
2. Production of Hybrid Seeds is costly
(a) Cost of hybrid seeds become expensive to the farmers.
(b) The information is genetically controlled from genetics of apomixes, which helps in transfer of "apomictic gene" into crop plants and produce hybrid seeds with desirable characters.
Click below to see answers of exercise question no 1 - 10 of Chapter 2, Sexual Reproduction in Flowering Plants
Chapter2, Sexual Reproduction in Flowering Plants - CBSE Class 12 Biology - NCERT Solutions
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